A standard motor-vehicle door latch has a pivotal latching fork, a release pawl engageable with the fork and displaceable between a latched position retaining the fork in a latched position engaged around a bolt and securing a motor-vehicle door closed and an unlatched position in which the fork can release the bolt and allow the door to open, and a release lever engageable with the pawl for displacing it between its positions and formed with an elongated slot. An outside actuating lever is provided with an entrainment nose aligned with an end of the release-lever slot. Separate inside and outside locking levers are coupled to a main locking lever displaceable thereby between a locked and an unlocked position. A link lever pivoted on the main locking lever carries a coupling pin projecting through the slot and engageable with the entrainment nose on pivoting of the main locking lever into the unlocked position of the main locking fever and unengageable on pivoting of the main locking lever with the entrainment nose into the locked position of the main locking lever. An antitheft lever displaceable between on and off positions is operatively engageable in the on position with the main locking lever to retain it in the locked position.
Normally the outside actuating lever is connected to the outside door handle and the inside actuating lever with the inside door handle. The outside locking lever is operated by a lock cylinder on the door and the inside locking lever is connected to an inside knob or element. With this system the outside actuating lever as well as the link lever decouple the actuating-lever system from the release lever in the locked position of the latch. Thus when locked the outside actuating lever can move but does nothing. The antitheft lever ensures when in the on position that when the door is locked it cannot even be opened by the inside handle.
Such a lock is described in German patent document 4,433,994 of Kleefeldt. The antitheft arrangement can move freely since the link lever is slidable on the main locking lever and is urged by a spring into the unlocked position. In the on position of the antitheft system a blocking formation is in the path of the link lever so that it cannot assume the unlocked position. In other words the movement of the antitheft system is defined by the link lever and the main locking lever.
In another known system the movement of the antitheft system is defined by the inside locking lever and the main locking lever. In this arrangement the link lever is no longer slidable on the main locking lever for the antitheft operation. This arrangement is advantageous but does not always function perfectly. If an attempt is made to move the latch out of the locked or antitheft position by means of the outside actuating lever, the coupling pin of the link lever engages laterally against the entrainment nose of the outside actuating lever and prevents the main locking lever from being fully moved in to the unlocked position. This blocks up the latch mechanism and, if too much force is applied to the handle, could damage it.